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논문 기본 정보

자료유형
학술저널
저자정보
Meyer, Roland (School of Engineering and Science, Jacobs University Bremen) Zhang, Xiangyang (ETH Zurich) Nau, Werner M. (School of Engineering and Science, Jacobs University Bremen)
저널정보
한국광과학회 Photochemical & photobiological sciences : an international journal Photochemical & photobiological sciences : an international journal 제8권 제12호
발행연도
2009.1
수록면
1,694 - 1,700 (7page)

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초록· 키워드

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Azoalkanes of the 2,3-diazabicyclo[2.2.2]-oct-2-ene type have been introduced as probes for antioxidants in homogeneous solution as well as in liposomes and micelles. The bimolecular fluorescence quenching of the bridgehead dichloro-substituted 1,4-dichloro-2,3-diazabicyclo[2.2.2]-oct-2-ene (3) was compared with that of the parent compound 2,3-diazabicyclo[2.2.2]-oct-2-ene (1) and the bridgehead-dialkylated compound 4-methyl-1-isopropyl-2,3-diazabicyclo[2.2.2]-oct-2-ene (2). Compound 3 showed a more efficient fluorescence quenching in C-H containing solvents (e.g., in n-hexane: 30 ns for 3 versus 340 ns for 1 and 770 ns for 2), but a less efficient quenching in aqueous solution (e.g., in deaerated $H_2O$: 485 ns for 3 versus 420 ns for 1 and 340 ns for 2), and also by molecular oxygen ($k_q/10^9M^{-1}s^{-1}$ = 0.32 for 3 versus 2.5 for 1 and 1.9 for 2). Towards low-molecular weight antioxidants, compound 3 showed a significantly higher reactivity (e.g., for reduced glutathione: $k_q/10^9M^{-1}s^{-1}$ = 1.8 for 3 versus 0.82 for 1 and 0.39 for 2), at the expense of a lower differentiation between the investigated antioxidants (lower selectivity). The increased reactivity of 3 and lower, as well as qualitatively different, selectivity is attributed to a combination of factors, most importantly the slightly increased excitation energy of 3 and its lower excited-state nucleophilicity. The latter was independently corroborated, besides its longer fluorescence lifetime in aqueous solution, through the trends in quenching rate constants of the azoalkanes 1.3 towards electron-deficient versus electron-rich lactone antioxidants of the benzofuranone type. While common inorganic buffer constituents caused no fluorescence quenching, significant quenching was observed, as a curiosity, for hydrogencarbonate ($k_q/10^6M^{-1}s^{-1}$ = 1.7 for 3 versus 2.4 for 1 and 0.45 for 2), with a fully manifested kinetic deuterium isotope effect ($k_q(H_2O)/k_q(D_2O)$ = 12) for 3.

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